Nitrogen-doped porous carbon material and preparation method and application thereof

ABSTRACT

A nitrogen-doped porous carbon material and a preparation method and an application thereof; wherein the nitrogen-doped porous carbon material has a specific surface area of 1600-3500 m 2 ·g −1 , mesopores with a pore size of 2-50 nm account for 20-40% of all pores, an average pore size is 2-20 nm, and a mass fraction of nitrogen atoms in the porous carbon material is 13.6-19.3 wt %. When being used as a supercapacitor material, the porous carbon material has a larger specific capacitance and a better capacitance retention rate. At a current density of 0.1 A·g −1 , the porous carbon material has a specific capacitance of about 847 F·g −1 . After 5000 cycles of charging and discharging, the capacitance retention rate is about 99.7%. Moreover, the porous carbon material features an excellent pore structure distribution, thus providing good CO 2  adsorption performance.

BACKGROUND Technical Field

The present invention belongs to the field of porous carbon materialpreparation technologies, and specifically, to a nitrogen-doped porouscarbon material and a preparation method and an application thereof.

Related Art

Information disclosed in the related art section is merely for betterunderstanding of the overall background of the present invention, andshould not be taken as an acknowledgement or any suggestion that theinformation constitutes the prior art that is well known to those ofordinary skill in the art.

A supercapacitor is a novel third-generation energy storage device aftermechanical energy storage and chemical energy storage. It has a powerdensity which is 10-100 times that of a battery, can achievehigh-current charging and discharging, and has the characteristics ofhigh charging and discharging efficiency and a long cycle life. Thesupercapacitor is highly demanded in the fields such as electronicproducts, power systems, vehicles, rail transit, aeronautics andastronautics, and has become a hot spot for studies of green energyconversion and secondary energy storage devices.

Porous carbon is the first choice material for current commercialsupercapacitor due to its advantages of a large specific surface area, awell-developed pore structure and good conductivity. The specificcapacitance of a carbon material can be increased to a certain extent byincreasing the specific surface area, but the relationship between theelectricity storage performance and the specific surface area is not asimple linear one. A purer carbon material has fewer functional groupson its surface, resulting in that its high specific surface area cannotbe fully utilized. Therefore, the method of increasing the specificcapacitance of the carbon material only by increasing the specificsurface area has great limitations. Modifying the carbon material byheteroatom doping is an effective method for improving the performanceof the porous carbon material. Nitrogen and carbon atoms have similaratomic radii. During doping, the structure of carbon is not easilydestroyed, and a six-membered ring structure of the carbon can bechanged to a five-membered ring structure to cause changes in thesurface structure, hydrophilicity and conductivity of the material,thereby greatly expanding the application fields of the carbon material.

Chinese Patent No. CN 108922794 A disclosed a method for preparing anitrogen-doped biomass-based activated carbon electrode material. Inthis method, the doping process is conducted before the thermochemicaltreatment process, so a large amount of the nitrogen source material isconsumed; and the thermochemical treatment requires a high temperatureand lasts for a long time, greatly increasing the costs of thepreparation process. The specific surface area of the carbon materialprepared by this method is 825.3 m²·g⁻¹. At a current density of 0.5A·g⁻¹, the specific capacitance is 259 F·g⁻¹, which still cannot meetthe criteria which current high-performance capacitor carbon needs tomeet.

Chinese Patent No. CN 108622877 A disclosed a nitrogen-doped porouscarbon material having a hierarchical pore structure and a preparationmethod and an application thereof. This method uses cellulosic biomassas the raw material and organic matter urea and glycine as nitrogensources and includes steps such as nitrogen source pretreatment, maxingof carbon and nitrogen sources, low-temperature carbonization, andhigh-temperature activation, which involves a complex process andconsumes a large amount of the nitrogen source material. The specificsurface area of the carbon material prepared by this method is 2600m²·g⁻¹. At a current density of 3 A·g⁻¹, the specific capacitance is 210F·g⁻¹, which cannot meet the criteria which current high-performancecapacitor carbon needs to meet.

Chinese Patent No. CN 108483442 A disclosed a method for preparing ahigh-mesoporosity nitrogen-doped carbon electrode material with bambooshoot shell. This method includes steps of hydrothermal pretreatment,simultaneous low-temperature carbonization and nitrogen doping, andactivation treatment, which involves a complex process and consumes alarge amount of the nitrogen source material. At a current density of0.5 A·g⁻¹, the specific capacitance is 209 F·g⁻¹, which cannot meet thecriteria which current high-performance capacitor carbon needs to meet.

Chinese Patent No. CN 109319778 A disclosed a preparation method and anapplication of a nitrogen-doped pine nut shell-based porous carbonmaterial, where chain nitrogen sources such as semicarbazide, urea, andguanidine carbonate are used as the nitrogen source material, a largeamount of dopant material is consumed, and the doping effect is notobvious. The pretreatment process adopts a low-temperature carbonizationprocess, which cannot completely remove volatiles in the raw material,and there are still a large number of H and O atoms in the carbonizedproduct, resulting in low efficiency in the doping process. At a currentdensity of 0.5 A·g⁻¹, the specific capacitance is 278-380 F·g⁻¹, andthere is still room for further improvement.

In the current related studies and patents, although a specific surfacearea of 300-2800 m²·g⁻¹ and a specific capacitance of up to 100-380F·g⁻¹ can be obtained by treating the biomass raw material, there arestill problems such as a complex preparation process, an unreasonableprocess flow, lack of diversified carbonaceous precursor raw materials,consumption of a large amount of nitrogen source material, lowefficiency in nitrogen doping, and an unstable doping structure. Thespecific capacitance still cannot meet the criteria which currenthigh-performance capacitor carbon needs to meet, and the doping methodis complex and not environmentally friendly.

SUMMARY

In view of the above technical problems in the prior art, objectives ofthe present invention are to provide a nitrogen-doped porous carbonmaterial and a preparation method and an application thereof.

In order to resolve the above technical problems, the present inventionadopts the following technical solution.

A first objective of the present invention is to provide anitrogen-doped porous carbon material, having a specific surface area of1600-3500 m²·g⁻¹, wherein mesopores with a pore size of 2-50 nm accountfor 20-40% of all pores, an average pore size is 2-20 nm, and a massfraction of nitrogen atoms in the porous carbon material is 13.6-19.3 wt%, which is much higher than those in current related patents. The highnitrogen content can effectively improve the surface structure,conductivity and wettability of the material, thereby improving theelectrochemical performance and the adsorption performance of thematerial.

When being used as a supercapacitor material, the porous carbon materialhas a larger specific capacitance and a better capacitance retentionrate. At a current density of 0.1 A·g⁻¹, the porous carbon material hasa specific capacitance of about 847 F·g⁻¹. After 5000 cycles of chargingand discharging, the capacitance retention rate is about 99.7%.

Moreover, the porous carbon material features an excellent porestructure distribution, thus providing good CO₂ adsorption performance.

A second objective of the present invention is to provide a method forpreparing a nitrogen-doped porous carbon material, including thefollowing steps:

washing, drying and pulverizing a carbonaceous precursor to obtainbiomass powder;

carbonizing the biomass powder at high temperature in an inert gas orammonia gas atmosphere, to obtain a carbonized product, wherein thetemperature of carbonization is 600-800° C.;

ultrasonically mixing and impregnating the carbonized product, asaturated chemical activator solution, and a nitrogen source material,wherein the nitrogen source material is melamine, polyaniline andpyridine; and

heating the impregnated product in an inert atmosphere for hybridizationto obtain biomass nitrogen-doped porous carbon.

Because the step of high-temperature carbonization is used in thepreparation process of the present invention, more volatiles and H and Oatoms are removed during the carbonization, thereby providing moreactive sites. The carbonized product is more easily bonded with N atomsin further reactions, thereby improving the efficiency of nitrogendoping, and reducing the amount of nitrogen source material required.Moreover, the high-temperature carbonization endows the carbonizedproduct with a higher porosity and a large pore size, which increasesthe contact area between the carbon material and the activator anddopant material, thereby facilitating the progress of the reaction.

The ammonia gas can provide amino to assist with the nitrogen dopingprocess. When the volatiles are separated out, nitrogen can be bondedwith the active sites left vacant on the carbon ring in a timely manner.

By heating the impregnated product in the inert atmosphere forhybridization, nitrogen atoms replace carbon atoms on the carbon ring,and a part of a five-membered ring structure is formed.

The inventor has found through experiments that a ring nitrogen sourcehas higher stability than a chain nitrogen source; when the ringnitrogen source such as melamine, polyaniline and pyridine is used fornitrogen doping of the porous carbon, a better stability of the porouscarbon material can be achieved by optimizing parameters of thepreparation process, and there is no significant decrease in thespecific capacitance even after thousands of times of charging anddischarging.

The ultrasonic treatment on the impregnated system can effectivelypromote mixing of the chemical activator and the nitrogen sourcematerial, thereby avoiding overly complex material pretreatmentprocedures (such as impregnation and mixing at high temperature,impregnation and mixing in a dilute solution followed by evaporation todryness, and pretreatment of the nitrogen source material followed byimpregnation and mixing), greatly shortening the treatment time, andimproving the treatment efficiency.

Under the joint action of the high-temperature carbonization, ultrasonicimpregnation and heating in the inert atmosphere for hybridization, theamount of biomass nitrogen doped in the porous carbon is greatlyincreased.

In some embodiments, the carbonaceous precursor includes but is notlimited to garlic stalk, sargassum, wood sawdust, fruit shell and straw.

In some embodiments, the carbonaceous precursor is passed through an 80mesh sieve after being pulverized. An excessively large particle sizecauses inadequate reaction of the material in subsequent steps, and anexcessively small particle size leads to increased preparation costs ofthe material.

In some embodiments, the time of the carbonization is 1.5-2.5 h.

In some embodiments, the saturated chemical activator solution is a KOHsaturated solution. The nitrogen source material in the presentinvention is insoluble in water, an excessively low concentrationaffects the efficiency of the impregnation process, and the KOHsaturated solution can ensure the full infiltration with KOH.

Further, a mass ratio of the carbonized product, the saturated chemicalactivator solution and the nitrogen source material is 1-3:1-5:0.1-2.The amount of the nitrogen source material used in the present inventionis small, a good nitrogen doping effect can be achieved.

Further, the temperature of the ultrasonic impregnation is roomtemperature.

Further, the frequency of the ultrasonic treatment is 10-50 kHz, powerof the ultrasonic treatment is 80-150 W, and the time of the ultrasonictreatment is 4-8 min.

In some embodiments, the temperature of the heating is 750-800° C., andthe time of the heating is 2-2.5 h.

In some embodiments, the preparation method further includes a step ofwashing and drying the obtained biomass nitrogen-doped porous carbon.The porous carbon is washed to remove impurities in the porous carbon.

Further, the obtained biomass nitrogen-doped porous carbon is pickledwith 10-20 wt % hydrochloric acid, and then is washed to neutrality withdeionized water.

A third objective of the present invention is to provide nitrogen-dopedporous carbon prepared by the above preparation method.

A fourth objective of the present invention is to provide an applicationof the above nitrogen-doped porous carbon in preparation of asupercapacitor material.

A fifth objective of the present invention is to provide an activatedcarbon electrode, where components of the activated carbon electrodeinclude the above nitrogen-doped porous carbon.

Further, the components of the activated carbon electrode furtherinclude a conductive agent and a binder, the conductive agent is carbonblack, acetylene black, graphite or other conductive additives or is acarbon nanotube additive, and the binder is polytetrafluoroethylene(PTFE), polyvinylidene fluoride (PVDF), polyvinyl alcohol,carboxymethylcellulose sodium, polyolefin, rubber or polyurethane.

A sixth objective of the present invention is to provide a method forpreparing the above activated carbon electrode, including the followingsteps:

adding a solvent to a mixture of the nitrogen-doped porous carbon, thebinder and the conductive agent to prepare a slurry;

evenly coating a current collector with the slurry and drying to obtainthe activated carbon electrode; or

hot-pressing the slurry to obtain the activated carbon electrode.

In some embodiments, the current collector is a copper foil, aluminumfoil, nickel mesh or stainless steel foil.

A seventh objective of the present invention is to provide anapplication of the above nitrogen-doped porous carbon in a CO₂adsorbent.

Beneficial effects of the present invention are as follows:

Because the step of high-temperature carbonization is used in thepreparation process of the present invention, more volatiles and H and Oatoms are removed during the carbonization, thereby providing moreactive sites. The carbonized product is more easily bonded with N atomsin further reactions, thereby improving the efficiency of nitrogendoping, and reducing the amount of nitrogen source material required.Moreover, the high-temperature carbonization endows the carbonizedproduct with a higher porosity and a large pore size, which increasesthe contact area between the carbon material and the activator anddopant material, thereby facilitating the progress of the reaction.

The molecular structure of the nitrogen source used in the presentinvention is ring-shaped, which has higher stability than a chainnitrogen source. The type of nitrogen doping in the porous carbonmaterial prepared by the process of the present invention is mainlypyrrole nitrogen and graphite nitrogen, which has a stable structure.Therefore, after thousands of times of charging and discharging, thereis no significant decrease in the specific capacitance of the material.

Optimized process steps are adopted in the present invention to avoidoverly complex material pretreatment procedures, and the introduction ofultrasonic treatment to mix the activator and the nitrogen sourcematerial greatly shortens the treatment time and improves the treatmentefficiency.

The present invention features a simple process, a wide range of rawmaterial sources, low costs, and a readily controllable reactionprocess, is suitable for scale production, and has a broad applicationprospect in the fields of supercapacitor electrode materials and CO₂adsorption materials, which is specifically embodied in the followingaspects: (1) The nitrogen-doped porous carbon material prepared by thetechnical process of the present invention has a three-dimensionalhierarchical pore structure with a specific surface area of 1600-3500m²·g⁻¹. (2) The nitrogen-doped porous carbon material has a largerspecific capacitance and better capacitance retention rate. To bespecific, when used as a supercapacitor electrode material, thenitrogen-doped porous carbon material has a specific capacitance of 847F·g⁻¹ at a current density of 0.1 A·g⁻¹, and after 5000 cycles ofcharging and discharging, the capacitance retention rate is 99.7%. (3)CO₂ adsorption tests show that the adsorption amounts of thenitrogen-doped porous carbon material at 25° C. and 0° C. arerespectively as high as 3.59 mmol/g and 6.11 mmol/g, exhibiting anexcellent pore structure distribution and an excellent CO₂ adsorptionperformance.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings that constitute a part of this application areused to provide a further understanding of this application. Exemplaryembodiments of this application and descriptions of the embodiments areused for describing this application, and do not constitute anyinappropriate limitation to this application.

FIG. 1 is a graph showing a nitrogen adsorption-desorption curveaccording to Embodiment 1 of the present invention;

FIG. 2 is a graph showing the distribution of pore sizes according toEmbodiment 1 of the present invention;

FIG. 3 is a graph showing the cycle performance according to Embodiment1 of the present invention;

FIG. 4 shows a cyclic voltammetric curve obtained by testing anelectrode material prepared in Embodiment 2 of the present invention ata scan rate of 200 mV·s⁻¹;

FIG. 5 shows a constant-current charging and discharging curve obtainedby testing the electrode material prepared in Embodiment 2 of thepresent invention at a current density of 5 A·g⁻¹;

FIG. 6 is a graph showing the rate capability of an electrode materialprepared in Embodiment 2 of the present invention; and

FIG. 7 is a scanning electron microscope (SEM) image of a nitrogen-dopedporous carbon material prepared in Embodiment 3 of the presentinvention.

DETAILED DESCRIPTION

It is to be noted that the following detailed descriptions are allexemplary and are intended to provide a further understanding of thisapplication. Unless otherwise specified, all technical and scientificterms used herein have the same meaning as commonly understood by thoseof ordinary skill in the art to which this application belongs.

It should be noted that terms used herein are only for describingspecific implementations and are not intended to limit exemplaryimplementations according to this application. As used herein, thesingular form is also intended to include the plural form unless thecontext clearly dictates otherwise. In addition, it should be furtherunderstood that, terms “comprise” and/or “include” used in thisspecification indicate that there are features, steps, operations,devices, components, and/or combinations thereof.

Embodiment 1

This embodiment relates to a method for preparing nitrogen-doped porouscarbon, including the following steps:

Step 1: Garlic stalk as the raw material was washed, placed in a blowdrying oven and dried at 120° C. for 48 h, pulverized, and passedthrough an 80 mesh sieve.

Step 2: The product obtained in the step 1 was placed in a tube furnacefor carbonization at 600° C. for 2 h. Nitrogen gas was used as an inertgas.

Step 3: The product obtained in the step 2 was washed and dried.

Step 4: The product obtained in the step 3, a KOH saturated solution andmelamine were mixed at a mass ratio of 1:4:0.2, and the mixture wasultrasonically treated for 6 min, wherein the ultrasonic frequency was40 kHz, and the power was 120 W.

Step 5: The product obtained in the step 4 was placed in a mufflefurnace for treatment at 800° C. for 2 h. Nitrogen gas was used as aninert gas.

Step 6: The product obtained in the step 5 was first pickled withhydrochloric acid, and then washed to neutrality with deionized water,and dried to obtain a nitrogen-doped biomass-based porous carbonmaterial.

Implementation effect: The mass ratio of nitrogen atoms of the productis as high as 19.3 wt %. The specific surface area calculated by the BETmethod is 2642 m²/g, the pore volume is 1.41 cm³/g, and the average poresize is 2.14 nm. The product is a carbon material having a high specificsurface area. A constant-current charging and discharging test wasperformed on a supercapacitor electrode material prepared by mixing thecarbon material, a conductive agent and a binder at a mass ratio of8:1:1, using 6 mol/L KOH as an electrolyte. At a current density of 0.1A/g, specific capacitance reaches 847 F/g. As shown in FIG. 6 , at acurrent density of 10 A/g, the specific capacitance can still reach 649F/g.

It may be learned from FIG. 1 that an isothermal adsorption-desorptioncurve of the material shows an obvious hysteresis loop, indicating thatthe material has a typical three-dimensional hierarchical porestructure. It may be learned from FIG. 2 that the material after beingdoped still has a large number of hierarchical structures. It may belearned from FIG. 3 that after 5000 cycles, the material can stillmaintain relatively high capacitance.

Embodiment 2

This embodiment relates to a method for preparing nitrogen-doped porouscarbon, including the following steps:

Step 1: Sargassum as the raw material was washed, placed in a blowdrying oven and dried at 120° C. for 48 h, pulverized, and passedthrough an 80 mesh sieve.

Step 2: The product obtained in the step 1 was placed in a tube furnace,heated to 800° C., and held at this temperature for 1.5 h. Argon gas wasused as an inert gas.

Step 3: The product obtained in the step 2 was washed and dried.

Step 4: The product obtained in the step 3, a KOH saturated solution andpolyaniline were mixed at a mass ratio of 1:5:0.3, and the mixture wasultrasonically treated for 10 min, wherein the ultrasonic frequency was50 kHz, and the power was 100 W.

Step 5: The product obtained in the step 4 was placed in a mufflefurnace for treatment at 750° C. for 2.5 h. Nitrogen gas was used as aninert gas.

Step 6: The product obtained in the step 5 was first pickled with 15 wt% hydrochloric acid, and then washed to neutrality with deionized water,and dried to obtain a nitrogen-doped biomass-based porous carbonmaterial.

Implementation effect: The mass ratio of nitrogen atoms of the productis up to 15.4 wt %. The specific surface area calculated by the BETmethod is 2543 m²/g, the pore volume is 1.52 cm³/g, and the average poresize is 2.39 nm. The product is a carbon material having a high specificsurface area. A constant-current charging and discharging test wasperformed on a supercapacitor electrode material prepared by mixing thecarbon material, a conductive agent and a binder at a mass ratio of8:1:1, using 6 mol/L KOH as an electrolyte. At a current density of 0.1A/g, specific capacitance reaches 594 F/g. At a current density of 10A/g, the specific capacitance can still reach 463 F/g.

It may be learned from the shapes in FIG. 4 and FIG. 5 that the cyclicvoltammetric curve of the material is approximately rectangular, and theconstant-current charging and discharging curve of the material exhibitsthe characteristics of an isosceles triangle, indicating that thematerial is mainly double-layer capacitance, and nitrogen dopingintroduces more structural nitrogen instead of nitrogen-containingfunctional groups. It may be learned from FIG. 6 that the capacitancevalue of the material can still remain stable at a large currentdensity, and the material has a good rate capability.

Embodiment 3

This embodiment relates to a method for preparing nitrogen-doped porouscarbon, including the following steps:

Step 1: Wood sawdust as the raw material was washed, placed in a blowdrying oven and dried at 105° C. for 72 h, pulverized, and passedthrough a 120 mesh sieve.

Step 2: The product obtained in the step 1 was placed in a tube furnaceand held at 600° C. for 2 h. Helium gas was used as an inert gas.

Step 3: The product obtained in the step 2 was washed and dried.

Step 4: The product obtained in the step 3 was mixed with a KOHsaturated solution at a mass ratio of 3:1 (carbon:activator) and withpyridine at a mass ratio of 1:7 (carbon:nitrogen source), and themixture was ultrasonically treated for 4 min, wherein the ultrasonicfrequency was 30 kHz, and the power was 140 W.

Step 5: The product obtained in the step 4 was placed in a mufflefurnace and held at 750° C. for 2.5 h. Ammonia gas was used as an inertgas.

Step 6: The product obtained in the step 5 was washed and dried toobtain a nitrogen-doped biomass-based porous carbon material.

Implementation effect: The mass ratio of nitrogen atoms of the productis up to 13.6 wt %. The specific surface area calculated by the BETmethod is 2098 m²/g, the pore volume is 1.40 cm³/g, and the average poresize is 2.14 nm. The product is a carbon material having a high specificsurface area. A constant-current charging and discharging test wasperformed on a supercapacitor electrode material prepared by mixing thecarbon material, a conductive agent and a binder at a mass ratio of8:1:1, using 6 mol/L KOH as an electrolyte. At a current density of 0.1A/g, specific capacitance reaches 330 F/g. At a current density of 10A/g, the specific capacitance can still reach 260 F/g.

FIG. 7 is an SEM image of a nitrogen-doped porous carbon materialprepared in Embodiment 3. It may be learned from the image that thematerial has abundant pore structures.

Embodiment 4

This embodiment relates to a method for preparing biomass-basednitrogen-doped porous carbon, including the following steps:

Step 1: Garlic stalk as the raw material was washed, placed in a blowdrying oven and dried at 120° C. for 48 h, pulverized, and passedthrough an 80 mesh sieve.

Step 2: The product obtained in the step 1 was placed in a tube furnacefor carbonization at 600° C. for 2 h. Nitrogen gas was used as an inertgas.

Step 3: The product obtained in the step 2 was washed and dried.

Step 4: The product obtained in the step 3, KOH and melamine were mixedat a mass ratio of 1:3:0.2, and the mixture was ultrasonically treatedfor 8 min, wherein the ultrasonic frequency was 10 kHz, and the powerwas 80 W.

Step 5: The product obtained in the step 4 was placed in a mufflefurnace for treatment at 800° C. for 2 h. Nitrogen gas was used as aninert gas.

Step 6: The product obtained in the step 5 was first pickled withhydrochloric acid, and then washed to neutrality with deionized water,and dried to obtain a nitrogen-doped biomass-based porous carbonmaterial.

Implementation effect: A CO₂ adsorption test on the product underatmospheric conditions indicates that the adsorption amounts at 25° C.and 0° C. are respectively as high as 3.59 mmol/g and 6.11 mmol/g, whichare quite high among the adsorption amounts of porous carbon materials.

Embodiment 5

This embodiment relates to a method for preparing biomass-basednitrogen-doped porous carbon, including the following steps:

Step 1: Wood sawdust as the raw material was washed, placed in a blowdrying oven and dried at 105° C. for 72 h, pulverized, and passedthrough a 120 mesh sieve.

Step 2: The product obtained in the step 1 was placed in a tube furnaceand held at 600° C. for 2 h. Helium gas was used as an inert gas.

Step 3: The product obtained in the step 2 was washed and dried.

Step 4: The product obtained in the step 3 was mixed with a KOHsaturated solution at a mass ratio of 3:1 (carbon:activator) and withpyridine at a mass ratio of 1:7 (carbon:nitrogen source), and themixture was ultrasonically treated for 5 min, wherein the ultrasonicfrequency was 50 kHz, and the power was 150 W.

Step 5: The product obtained in the step 4 was placed in a mufflefurnace and held at 750° C. for 2.5 h. Ammonia gas was used as an inertgas.

Step 6: The product obtained in the step 5 was washed and dried toobtain a nitrogen-doped biomass-based porous carbon material.

Implementation effect: A CO₂ adsorption test on the product underatmospheric conditions indicates that the adsorption amounts at 25° C.and 0° C. are respectively as high as 3.86 mmol/g and 6.17 mmol/g, whichare quite high among the adsorption amounts of porous carbon materials.

TABLE 1 Statistics on carbon sources, nitrogen sources, methods andnitrogen doping effects in nitrogen doping patents Carbon NitrogenNitrogen Patent number source source Method content CN Water MelaminePremixing, low-temperature 5-9 wt % 107055531 A chestnut carbonization,activation CN Reed rod Nitrogen Hydrothermal carbonization, 6-8 at. %107010624 A fertilizer activation CN Soybean Soybean meal KOH activation5.63 at. % 106517183 A meal CN Peanut shell Melamine Ball milling, 8-10at. % 106629724 A low-temperature pre-carbonization, KOH activation CNSoy fiber Soy fiber Template method, potassium 4.56 at. % 108940191 Aoxalate activation CN Biomass Biomass One-step “foaming method” 3.6 at.% 106006636 A CN Cottonseed Urea NaOH one-step activation 1.84-7.35 at.% 108455597 A husk The present Carbon-rich Melamine, High-temperature13.6-19.3 wt % invention precursor polyaniline, carbonization, pyrrole,high-temperature KOH pyridine activation, hybridization

Table 1 shows relevant information about carbon sources, nitrogensources, doping methods and doping efficiency in nitrogen doping carbonmaterial patents in recent years collected by the inventor. It is foundthrough statistics that the existing nitrogen doping processes stillhave the problems of complex process and low doping efficiency.

The foregoing descriptions are merely preferred embodiments of thisapplication, but are not intended to limit this application. Thoseskilled in the art may make various modifications and changes to thisapplication. Any modification, equivalent replacement, or improvementmade without departing from the spirit and principle of this applicationshall fall within the protection scope of this application.

1. A nitrogen-doped porous carbon material, having a specific surfacearea of 1600-3500 m²·g⁻¹, wherein mesopores with a pore size of 2-50 nmaccount for 20-40% of all pores, an average pore size is 2-20 nm, and amass fraction of nitrogen atoms in the porous carbon material is13.6-19.3 wt %.
 2. A method for preparing a nitrogen-doped porous carbonmaterial, comprising the following steps: washing, drying andpulverizing a carbonaceous precursor to obtain biomass powder;carbonizing the biomass powder at high temperature in an inert gas orammonia gas atmosphere, to obtain a carbonized product, wherein thetemperature of carbonization is 600-800° C.; ultrasonically mixing andimpregnating the carbonized product, a saturated chemical activatorsolution, and a nitrogen source material, wherein the nitrogen sourcematerial is melamine, polyaniline or pyridine; and heating theimpregnated product in an inert atmosphere to obtain biomassnitrogen-doped porous carbon.
 3. The method for preparing anitrogen-doped porous carbon material according to claim 2, wherein thecarbonaceous precursor comprises but is not limited to garlic stalk,sargassum, wood sawdust, fruit shell and straw; the carbonaceousprecursor is passed through an 80 mesh sieve after being pulverized; thetime of the carbonization is 1.5-2.5 h; the saturated chemical activatorsolution is a KOH saturated solution; and a mass ratio of the carbonizedproduct, the saturated chemical activator solution and the nitrogensource material is 1-3:1-5:0.1-2.
 4. The method for preparing anitrogen-doped porous carbon material according to claim 2, wherein thefrequency of the ultrasonic treatment is 10-50 kHz, power of theultrasonic treatment is 80-150 W, and the time of the ultrasonictreatment is 4-8 min.
 5. The method for preparing a nitrogen-dopedporous carbon material according to claim 2, wherein the temperature ofthe heating is 750-800° C., and the time of the heating is 2-2.5 h; thepreparation method further comprises a step of washing and drying theobtained biomass nitrogen-doped porous carbon; and the obtained biomassnitrogen-doped porous carbon is pickled with 10-20 wt % hydrochloricacid, and then is washed to neutrality with deionized water.
 6. Anitrogen-doped porous carbon prepared by the preparation methodaccording to claim
 2. 7. A method comprising applying the nitrogen-dopedporous carbon according to claim 6 in preparation of a supercapacitormaterial.
 8. An activated carbon electrode, wherein components of theactivated carbon electrode comprise the nitrogen-doped porous carbonaccording to claim 6; and further, the components of the activatedcarbon electrode further comprise a conductive agent and a binder, theconductive agent is carbon black, acetylene black, graphite or otherconductive additives or is a carbon nanotube additive, and the binder ispolytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF),polyvinyl alcohol, carboxymethylcellulose sodium, polyolefin, rubber orpolyurethane.
 9. A method for preparing the activated carbon electrodeaccording to claim 8, comprising the following steps: adding a solventto a mixture of the nitrogen-doped porous carbon, the binder and theconductive agent to prepare a slurry; and evenly coating a currentcollector with the slurry and drying to obtain the activated carbonelectrode; or hot-pressing the slurry to obtain the activated carbonelectrode.
 10. An application of the nitrogen-doped porous carbonaccording to claim 6 in a CO₂ adsorbent.